1. Field of the Invention
The present invention relates to a method of controlling impedance of vias, and more particularly to a method of controlling impedance of vias for efficiently maintaining signal integrity and increasing signal transmission speed.
2. General Background
Conventionally, there has been a high-frequency multilayer circuit substrate, in which transmission lines are connected by way of vias provided for the improvement in performance of a high-frequency circuit and for high-density mounting. As reduction in size and increase in transmission signal frequency of this multilayer circuit substrate have been needed, a transmission loss due to signal wave reflection in the transmission lines and via connecting portion have become a more serious problem. These may harm integrity of the signals. Stray capacitance and parasitic inductance of the vias always exist. The stray capacitance may delay a rising time of the signal and decrease a transmitting speed of the signal. The parasitic inductance may weaken shunt capacitors mounted on the circuit substrate and lead to a poor filter performance of the circuit substrate. The high-frequency multilayer circuit substrate is required to control the characteristic impedance of the vias.
What is desired, therefore, is a method of controlling impedance of vias which can efficiently maintaining signal integrity and increase signal transmission speed.